Maria Sakkari became the first top-10 seed to exit the French Open as she fell in straight sets to Karolina Muchova in a battling encounter.

It is the second successive year that Sakkari - a previous semi-finalist at Roland Garros - has been knocked out of the clay-court Grand Slam by Muchova.

"It's a little bit of deja vu," world number 43 Muchova said.

"It was a very tough match, she is a very good player. I'm glad we didn't play a [second] tie-break, I managed the nerves."

Muchova has beaten five top-10 players in 16 Grand Slam tournaments, including then world number one Ashleigh Barty at the 2021 Australian Open.

However she struggled with abdominal and ankle injuries in 2022, which limited her playing time.

"I don't want to say I'm not focused on other tournaments, but the motivation is bigger at all the four slams," Muchova, the world number 43, told reporters.

"I'm trying to get back my ranking as well because I think I could be at least seeded at the Grand Slams."

Muchova will face Argentina's Nadia Podoroska in the second round in Paris.

Pegula progresses on first day in Paris

Third seed Jessica Pegula progressed to the second round with a scrappy 6-4 6-2 win over American compatriot Danielle Collins.

Pegula has yet to go beyond the quarter-finals of a Grand Slam singles event but came out on top against Collins in a match that had nine breaks of serve.

She will face Camila Giorgi next after the Italian beat home favourite Alize Cornet 6-3 6-4.

Pegula and Collins were the last match on Court Suzanne Lenglen, with Pegula saying it was "not easy" to wait for other matches to finish before taking to the court.

"For some reason I felt like I needed some extra time so I took a nap - I was able to feel pretty good before I came out here," she said.

"It's never easy, especially waiting all day after Karen [Khachanov] went five sets in the first match and then there were tough matches to follow.

"Thanks to [Andrey] Rublev for not going to five because that would have been really tough."

Sunday's opening day of action also brought defeat for 21st seed Magda Linette as the Pole was defeated 6-3 1-6 6-3 by Canada's 2021 US Open finalist Leylah Fernandez.

Poland could celebrate victory elsewhere, however, as Magdalena Frech stunned China's Zhang Shuai 6-1 6-1, while Belgium's 28th seed Elise Mertens beat Viktoria Hruncakova 6-1 6-4.

Chinese 19th seed Qinwen Zheng progressed with a 6-3 6-1 win over Tamara Zidansek.